{"id":"CVE-2026-85091","state":"PUBLISHED","title":"zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate","description":"zlib versions 1.3.1.2 through 1.3.2 contain a heap buffer overflow vulnerability in the gz_vacate() function when processing non-blocking gzwrite() operations with stale external buffer pointers. Attackers can trigger the overflow by calling gzprintf() or gzvprintf() after a write stall, causing an unchecked memmove() to write beyond the internal input buffer boundary.","publishedAt":"2026-09-03T01:04:44.460Z","updatedAt":"2026-09-03T13:21:30.355Z","severity":{"score":8.3,"label":"High","version":"4.0","vector":"CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N","source":"VulnCheck"},"assigner":"VulnCheck","products":["zlib zlib"],"affected":[{"vendor":"zlib","product":"zlib","packageURL":"pkg:github/madler/zlib","defaultStatus":"unaffected","versions":[{"version":"1.3.1.2","status":"affected","lessThanOrEqual":"1.3.2","versionType":"custom"}]}],"references":["https://gist.github.com/thesmartshadow/e0b9481792afb7c31e86fee1ff084490","https://github.com/madler/zlib/blob/v1.3.2/gzwrite.c#L393","https://github.com/madler/zlib","https://www.vulncheck.com/advisories/zlib-1.3.1.2-through-1.3.2-heap-buffer-overflow-via-gz-vacate"],"weaknesses":["CWE-787"],"ingestedAt":"2026-10-29T20:13:15.269Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/85xxx/CVE-2026-85091.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-85091","state":"PUBLISHED","datePublished":"2026-09-03T01:04:44.460Z","dateUpdated":"2026-09-03T13:21:30.355Z","assignerShortName":"VulnCheck","assignerOrgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","dateReserved":"2026-09-02T23:53:05.582Z"},"containers":{"cna":{"title":"zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate","descriptions":[{"lang":"en","value":"zlib versions 1.3.1.2 through 1.3.2 contain a heap buffer overflow vulnerability in the gz_vacate() function when processing non-blocking gzwrite() operations with stale external buffer pointers. Attackers can trigger the overflow by calling gzprintf() or gzvprintf() after a write stall, causing an unchecked memmove() to write beyond the internal input buffer boundary."}],"affected":[{"vendor":"zlib","product":"zlib","packageURL":"pkg:github/madler/zlib","defaultStatus":"unaffected","versions":[{"version":"1.3.1.2","status":"affected","lessThanOrEqual":"1.3.2","versionType":"custom"}]}],"references":[{"url":"https://gist.github.com/thesmartshadow/e0b9481792afb7c31e86fee1ff084490","name":"Technical report and proof of concept","tags":["technical-description","exploit"]},{"url":"https://github.com/madler/zlib/blob/v1.3.2/gzwrite.c#L393","tags":["technical-description"]},{"url":"https://github.com/madler/zlib","tags":["product"]},{"url":"https://www.vulncheck.com/advisories/zlib-1.3.1.2-through-1.3.2-heap-buffer-overflow-via-gz-vacate","name":"VulnCheck Advisory: zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate","tags":["third-party-advisory"]}],"metrics":[{"cvssV4_0":{"version":"4.0","vectorString":"CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N","baseScore":8.3,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"HIGH","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"HIGH","vulnAvailabilityImpact":"HIGH","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE"}},{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H","baseScore":7.4,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"HIGH","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"HIGH","availabilityImpact":"HIGH"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-787","lang":"en","description":"Out-of-bounds Write","type":"CWE"}]}],"providerMetadata":{"shortName":"VulnCheck","orgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","dateUpdated":"2026-09-03T01:04:44.460Z"},"datePublic":"2026-09-02T00:00:00.000Z","cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:zlib:zlib:*:*:*:*:*:*:*:*","versionStartIncluding":"1.3.1.2","versionEndIncluding":"1.3.2"}]}]}],"credits":[{"lang":"en","value":"Ali Firas (thesmartshadow)","type":"finder"}],"x_generator":{"engine":"vulncheck-endgame"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-03T13:21:12.950523Z","id":"CVE-2026-85091","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-09-03T13:21:30.355Z"}}]}}}